Many communications systems have the ability to provide intercept services. Intercept services are services for intercepting calls and providing an eavesdropping capability. These services are typically used by law enforcement agencies (LEA) within their jurisdictions.
When a particular telephone line in a wireline telephony system is to be targeted for intercept, an indication of the line number is included in a list of numbers to be monitored. Similarly, within existing mobile telephony systems, a user number or telephone number is specified for intercept, and included with all such numbers. In prior art telephony systems, either wireline or mobile, intercept target lists are created and maintained manually in a controlled environment, and are subsequently loaded into the network switches. The intercept target lists typically include information describing the user to be monitored and the monitoring agency to which the monitored traffic should be delivered. When a call is placed through a network switch which has been loaded with an intercept target list, or when another appropriate event within the call process occurs, the switch queries the intercept target list to determine if any list member is involved in the call. If a user involved in the call is found in the list, the switch invokes a monitoring function which forwards the call to the appropriate monitoring agency. This prior art method of determining whether to intercept a call is herein identified as user-based intercept. In user-based intercept, the decision whether or not to intercept any call is based on the identity of either the calling party or the called party.
The party identity is typically given by what is referred to as the telephone number. This existing monitoring capability limits the intercept functionality such that it is only the telephone number which is used to perform the intercept determination.
A growing number of monitoring agencies desire to make call monitoring decisions based on criteria other than the identity of users or their associated telephone numbers. For example, sovereign entities may want to monitor all calls that emanate from, or terminate in, a certain location area or region. This type of intercept decision based on location is herein referred to as location-based intercept. Unfortunately, prior art switches supporting user-based intercept do not provide for location-based intercept. In order to provide intercept of all calls in any given area using existing switches and their associated intercept target lists, it would be necessary to include all users in the area in the intercept target list. This is not feasible because intercept target lists in switches are of a fixed size and cannot accommodate enough entries.
In order to accommodate intercept based on criteria other than user identities, new switches could be designed or current switches could be modified; however, this would be a very expensive solution to the problem. There is a large installed base of existing switches in communications systems today, and the cost of upgrading or replacing them all just to modify the intercept decision would be prohibitive. It would be desirable for existing switches to accommodate location-based intercept.
What is needed is a method and apparatus for providing location-based intercept with switches already having user-based intercept capability.